+.BR \-\-exclude=(true|false|all|flag)
+
+A message is called "excluded" if it matches at least one tag in
+search.tag_exclude that does not appear explicitly in the search terms.
+This option specifies whether to omit excluded messages in the search
+process.
+
+The default value,
+.BR true ,
+prevents excluded messages from matching the search terms.
+
+.B all
+additionally prevents excluded messages from appearing in displayed
+results, in effect behaving as though the excluded messages do not exist.
+
+.B false
+allows excluded messages to match search terms and appear in displayed
+results. Excluded messages are still marked in the relevant outputs.
+
+.B flag
+only has an effect when
+.BR --output=summary .
+The output is almost identical to
+.BR false ,
+but the "match count" is the number of matching non-excluded messages in the
+thread, rather than the number of matching messages.
+.RE